The Uninhabitable Earth

mardi 5 septembre 2017

THE UNINHABITABLE EARTH

Famine, economic collapse, a sun that cooks us : What climate change could wreak — sooner than you think.

I. ‘Doomsday’

Peering beyond scientific reticence.

It is, I promise, worse than you think. If your anxiety about global warming is dominated by fears of sea-level rise, you are barely scratching the surface of what terrors are possible, even within the lifetime of a teenager today. And yet the swelling seas — and the cities they will drown — have so dominated the picture of global warming, and so overwhelmed our capacity for climate panic, that they have occluded our perception of other threats, many much closer at hand. Rising oceans are bad, in fact very bad ; but fleeing the coastline will not be enough.

Indeed, absent a significant adjustment to how billions of humans conduct their lives, parts of the Earth will likely become close to uninhabitable, and other parts horrifically inhospitable, as soon as the end of this century.

The Earth has experienced five mass extinctions before the one we are living through now, each so complete a slate-wiping of the evolutionary record it functioned as a resetting of the planetary clock, and many climate scientists will tell you they are the best analog for the ecological future we are diving headlong into. Unless you are a teenager, you probably read in your high-school textbooks that these extinctions were the result of asteroids. In fact, all but the one that killed the dinosaurs were caused by climate change produced by greenhouse gas. The most notorious was 252 million years ago ; it began when carbon warmed the planet by five degrees, accelerated when that warming triggered the release of methane in the Arctic, and ended with 97 percent of all life on Earth dead. We are currently adding carbon to the atmosphere at a considerably faster rate ; by most estimates, at least ten times faster. The rate is accelerating. This is what Stephen Hawking had in mind when he said, this spring, that the species needs to colonize other planets in the next century to survive, and what drove Elon Musk, last month, to unveil his plans to build a Mars habitat in 40 to 100 years. These are nonspecialists, of course, and probably as inclined to irrational panic as you or I. But the many sober-minded scientists I interviewed over the past several months — the most credentialed and tenured in the field, few of them inclined to alarmism and many advisers to the IPCC who nevertheless criticize its conservatism — have quietly reached an apocalyptic conclusion, too : No plausible program of emissions reductions alone can prevent climate disaster.

Over the past few decades, the term “Anthropocene” has climbed out of academic discourse and into the popular imagination — a name given to the geologic era we live in now, and a way to signal that it is a new era, defined on the wall chart of deep history by human intervention. One problem with the term is that it implies a conquest of nature (and even echoes the biblical “dominion”). And however sanguine you might be about the proposition that we have already ravaged the natural world, which we surely have, it is another thing entirely to consider the possibility that we have only provoked it, engineering first in ignorance and then in denial a climate system that will now go to war with us for many centuries, perhaps until it destroys us. That is what Wallace Smith Broecker, the avuncular oceanographer who coined the term “global warming,” means when he calls the planet an “angry beast.” You could also go with “war machine.” Each day we arm it

II. Heat Death

The bahraining of New York.

Humans, like all mammals, are heat engines ; surviving means having to continually cool off, like panting dogs. For that, the temperature needs to be low enough for the air to act as a kind of refrigerant, drawing heat off the skin so the engine can keep pumping. At seven degrees of warming, that would become impossible for large portions of the planet’s equatorial band, and especially the tropics, where humidity adds to the problem ; in the jungles of Costa Rica, for instance, where humidity routinely tops 90 percent, simply moving around outside when it’s over 105 degrees Fahrenheit would be lethal. And the effect would be fast : Within a few hours, a human body would be cooked to death from both inside and out.

Climate-change skeptics point out that the planet has warmed and cooled many times before, but the climate window that has allowed for human life is very narrow, even by the standards of planetary history. At 11 or 12 degrees of warming, more than half the world’s population, as distributed today, would die of direct heat. Things almost certainly won’t get that hot this century, though models of unabated emissions do bring us that far eventually.

At present, most regions reach a wet-bulb maximum of 26 or 27 degrees Celsius ; the true red line for habitability is 35 degrees. What is called heat stress comes much sooner.

III. The End of Food

Praying for cornfields in the tundra.

Climates differ and plants vary, but the basic rule for staple cereal crops grown at optimal temperature is that for every degree of warming, yields decline by 10 percent. Some estimates run as high as 15 or even 17 percent. Which means that if the planet is five degrees warmer at the end of the century, we may have as many as 50 percent more people to feed and 50 percent less grain to give them. And proteins are worse : It takes 16 calories of grain to produce just a single calorie of hamburger meat, butchered from a cow that spent its life polluting the climate with methane farts.

Pollyannaish plant physiologists will point out that the cereal-crop math applies only to those regions already at peak growing temperature, and they are right — theoretically, a warmer climate will make it easier to grow corn in Greenland. But as the pathbreaking work by Rosamond Naylor and David Battisti has shown, the tropics are already too hot to efficiently grow grain, and those places where grain is produced today are already at optimal growing temperature — which means even a small warming will push them down the slope of declining productivity. And you can’t easily move croplands north a few hundred miles, because yields in places like remote Canada and Russia are limited by the quality of soil there ; it takes many centuries for the planet to produce optimally fertile dirt.

IV. Climate Plagues

What happens when the bubonic ice melts ?

Rock, in the right spot, is a record of planetary history, eras as long as millions of years flattened by the forces of geological time into strata with amplitudes of just inches, or just an inch, or even less. Ice works that way, too, as a climate ledger, but it is also frozen history, some of which can be reanimated when unfrozen. There are now, trapped in Arctic ice, diseases that have not circulated in the air for millions of years — in some cases, since before humans were around to encounter them. Which means our immune systems would have no idea how to fight back when those prehistoric plagues emerge from the ice.

V. Unbreathable Air

A rolling death smog that suffocates millions.

Our lungs need oxygen, but that is only a fraction of what we breathe. The fraction of carbon dioxide is growing : It just crossed 400 parts per million, and high-end estimates extrapolating from current trends suggest it will hit 1,000 ppm by 2100. At that concentration, compared to the air we breathe now, human cognitive ability declines by 21 percent.

Already, more than 10,000 people die each day from the small particles emitted from fossil-fuel burning ; each year, 339,000 people die from wildfire smoke, in part because climate change has extended forest-fire season (in the U.S., it’s increased by 78 days since 1970). By 2050, according to the U.S. Forest Service, wildfires will be twice as destructive as they are today ; in some places, the area burned could grow fivefold. What worries people even more is the effect that would have on emissions, especially when the fires ravage forests arising out of peat.

VI. Perpetual War

The violence baked into heat.

Climatologists are very careful when talking about Syria. They want you to know that while climate change did produce a drought that contributed to civil war, it is not exactly fair to say that the conflict is the result of warming ; next door, for instance, Lebanon suffered the same crop failures. But researchers like Marshall Burke and Solomon Hsiang have managed to quantify some of the non-obvious relationships between temperature and violence : For every half-degree of warming, they say, societies will see between a 10 and 20 percent increase in the likelihood of armed conflict. In climate science, nothing is simple, but the arithmetic is harrowing : A planet five degrees warmer would have at least half again as many wars as we do today. Overall, social conflict could more than double this century.

This is one reason that, as nearly every climate scientist I spoke to pointed out, the U.S. military is obsessed with climate change : The drowning of all American Navy bases by sea-level rise is trouble enough, but being the world’s policeman is quite a bit harder when the crime rate doubles. Of course, it’s not just Syria where climate has contributed to conflict. Some speculate that the elevated level of strife across the Middle East over the past generation reflects the pressures of global warming — a hypothesis all the more cruel considering that warming began accelerating when the industrialized world extracted and then burned the region’s oil.

VII. Permanent Economic Collapse

Dismal capitalism in a half-poorer world.

The murmuring mantra of global neoliberalism, which prevailed between the end of the Cold War and the onset of the Great Recession, is that economic growth would save us from anything and everything.But in the aftermath of the 2008 crash, a growing number of historians studying what they call “fossil capitalism” have begun to suggest that the entire history of swift economic growth, which began somewhat suddenly in the 18th century, is not the result of innovation or trade or the dynamics of global capitalism but simply our discovery of fossil fuels and all their raw power — a onetime injection of new “value” into a system that had previously been characterized by global subsistence living. Before fossil fuels, nobody lived better than their parents or grandparents or ancestors from 500 years before, except in the immediate aftermath of a great plague like the Black Death, which allowed the lucky survivors to gobble up the resources liberated by mass graves. After we’ve burned all the fossil fuels, these scholars suggest, perhaps we will return to a “steady state” global economy. Of course, that onetime injection has a devastating long-term cost : climate change.

VIII. Poisoned Oceans

Sulfide burps off the skeleton coast.

That the sea will become a killer is a given. Barring a radical reduction of emissions, we will see at least four feet of sea-level rise and possibly ten by the end of the century. A third of the world’s major cities are on the coast, not to mention its power plants, ports, navy bases, farmlands, fisheries, river deltas, marshlands, and rice-paddy empires, and even those above ten feet will flood much more easily, and much more regularly, if the water gets that high. At least 600 million people live within ten meters of sea level today.

But the drowning of those homelands is just the start. At present, more than a third of the world’s carbon is sucked up by the oceans — thank God, or else we’d have that much more warming already. But the result is what’s called “ocean acidification,” which, on its own, may add a half a degree to warming this century. It is also already burning through the planet’s water basins — you may remember these as the place where life arose in the first place.

That isn’t all that ocean acidification can do. Carbon absorption can initiate a feedback loop in which underoxygenated waters breed different kinds of microbes that turn the water still more “anoxic,” first in deep ocean “dead zones,” then gradually up toward the surface. There, the small fish die out, unable to breathe, which means oxygen-eating bacteria thrive, and the feedback loop doubles back.

IX. The Great Filter

Our present eeriness cannot last.

So why can’t we see it ? In his recent book-length essay The Great Derangement, the Indian novelist Amitav Ghosh wonders why global warming and natural disaster haven’t become major subjects of contemporary fiction — why we don’t seem able to imagine climate catastrophe, and why we haven’t yet had a spate of novels in the genre he basically imagines into half-existence and names “the environmental uncanny.”

Surely this blindness will not last — the world we are about to inhabit will not permit it. In a six-degree-warmer world, the Earth’s ecosystem will boil with so many natural disasters that we will just start calling them “weather” : a constant swarm of out-of-control typhoons and tornadoes and floods and droughts, the planet assaulted regularly with climate events that not so long ago destroyed whole civilizations. The strongest hurricanes will come more often, and we’ll have to invent new categories with which to describe them ; tornadoes will grow longer and wider and strike much more frequently, and hail rocks will quadruple in size. Humans used to watch the weather to prophesy the future ; going forward, we will see in its wrath the vengeance of the past. Early naturalists talked often about “deep time” — the perception they had, contemplating the grandeur of this valley or that rock basin, of the profound slowness of nature. What lies in store for us is more like what the Victorian anthropologists identified as “dreamtime,” or “everywhen” : the semi-mythical experience, described by Aboriginal Australians, of encountering, in the present moment, an out-of-time past, when ancestors, heroes, and demigods crowded an epic stage. You can find it already watching footage of an iceberg collapsing into the sea — a feeling of history happening all at once.